It is known that the topping for a pizza may vary greatly according to different consumer tastes and according to the imagination of the maker. Therefore, other ingredients are often added to the basic topping, such as anchovies, tuna, seafoods, olives, artichokes, various chopped vegetables, appropriately sliced sausage products, mushrooms, pickles, cheeses, eggs. The term "ready-to-eat pizza" is intended to refer to a pizza that, once removed from the container in which it had been packaged and stored, requires simply to be heated to be as tasty and appetizing as when it was fresh out of the oven.
For the industrial production of ready-to-eat pizzas as, in general, for the production of other items of ready-to-eat food products, it is necessary to comply with a dual requirement, that is, on the one hand, to ensure that the pizza is non-toxic and keeps well and, on the other hand, to keep the physical and organoleptic properties of the pizza as close as possible to those of freshly prepared pizza straight from the oven.
In order to ensure that food products in general and cooked, ready-to-eat food products in particular are nontoxic and keep well, prior art practices teach that the products should be sterilized or pasteurized by appropriate heat treatments which, in some fortunate cases, may coincide with the cooking processes themselves.
In the case of pizza, non-toxicity and keeping capacity must be ensured for all components (base and toppings) which, it is known, may each have very different natural characteristics and intrinsic behaviour patterns.
In order to prepare a good pizza, that is one which can compare organoleptically with those prepared and eaten immediately in a pizzeria, it is necessary that the base be cooked (in an oven) at a high temperature (350.degree./400.degree. C.) for a very short time, about 2-3 minutes. When it is taken out of the oven after such treatment, the pizza base has a crispy crust and a moist interior.
However the above heat treatment is not long enough to pasteurize the ingredients of the pizza topping which, as is well known, for this purpose need to be heated throughout to about 90.degree.-95.degree. C. for at least 10 minutes.
If a pizza prepared as in a pizzeria were to be cooled, packaged and kept at a low temperature, for example at 8.degree. C.-10.degree. C. (chilled) it would be entirely unstable from a bacteriological point of view and would need to be disposed of after about 5-6 days owing to an unstoppable growth of bacterial flora.
However, should the above cooking process be lengthened in order to comply with the pasteurizing requirements of the topping ingredients, the base would be too dry and organoleptically unacceptable.